The implication of Streptococcus sanguis in the process of caries formation, and the apparent intimate involvement of the microbial dextran in this process indicates that a thorough investigation of the enzyme responsible for i-s synthesis should be carried out. Dextran sucrase, an extracellular enzyme which catalyzes the transfer of glucose from sucrose to the growing dextran, is to be investigated, with regard to its mechanism, and the pathyway of the reaction it catalyzes. The purpose of these studies is to provide an understanding of the reaction so that a rational approach to the design of effective inhibitors can be made. The enzyme is to be purified to homogeneity, so that the protein is free of contaminating proteins as well as endogeneous substrate. Once purified the mechanism will be explored in experiments designed to test the occurrence of a glycosyl enzyme intermediate, or a carbonium ion intermediate. In addition the functional groups that are involved in catalysis will be examined in experiments involving the modification of the protein with specific reagents. Several aspects of the reaction patyway are to be investigated. These include the mechanism by which dextran chains are initiated, the direction in which the chains grow, and the mechanism by which branches are introduced into the polymer. BIBLIOGRAPHIC REFERENCES: Structural Characteristics of Native and Enzymically Formed Dextran of S. sanguis ATCC 10558. Alice T. Arnett and Robert M. Mayer Carb. Res. 42 (1975) 339-345.